1. Field of the Invention
The invention relates to the fields of magnetic and superconductive materials and pertains to a magnetic levitation device as can be used, for example with superconductive contactless transport devices or linear or radial levitation bearings.
2. Discussion of Background Information
Superconductive magnetic levitation devices require a guide track or fixed counterbearing, which provide a magnetic field that is constant along the direction of movement, but perpendicular thereto has a sharp field gradient. The superconductors attached in the movable part (transport car) can adopt a stable position in this magnetic field if they are hard type II superconductors.
Magnetic fields can penetrate type II superconductors in the form of quantized magnetic flux lines that can be held in the superconducting matrix by nanoscale deposits or construction errors. It is thus possible to firmly anchor external magnetic field configurations in a superconductor of this type. If the magnetic field generated by the guide track is anchored in the superconductor at a fixed distance from the guide track from the normal conducting into the superconducting state due to the cooling of the superconductor, the superconductor responds to a deflection from the cooling position with restoring forces that draw the superconductor back into it. The restoring forces are dependent on the change of the magnetic field and thus also on the size of the deflection. The larger the change in the magnetic field, the larger the restoring force.
With superconductive magnetic levitation devices in contactless transport devices and linear or curved levitation bearings, the stability of a certain position in the vertical as well as in the horizontal direction is very important, in addition to the lift force. A measure of the stability is the stiffness in a marked direction. This is given in N/mm and describes what force is necessary to displace the movable part of the magnetic levitation device by 1 mm. However, since the forces are dependent on precisely the deflection around the cooling position, it is not possible to meet high demands in terms of the stiffness of a position with high complete reversal of stress.
With deflections from the cooling position, the increase of the repelling force is disproportionately high, so that for greater deflections, greater forces and stiffnesses can be achieved. In order to achieve a greater stiffness for a transport device, the levitation device is “prestressed.” According to the prior art, this is achieved through a high service weight of the transport device compared to the payload. However, this leads to a high energy consumption by the drive unit.
A general overview of the application of hard type II superconductors in magnetic levitation systems and radial bearings is provided by L. Schultz et al. (Z. Metallkd. 93 (10) 1057-1064 (2002)). J. Hull et al. (J. Appl. Phys. 86 (11) 6396 (1999)) shows analytically that the stiffness in the lateral direction present for a certain cooling position is always half of that in the vertical direction. J. Wang et al. (Physica C 378-381 (1) 809-814 (2002)) describe the design of a new levitation system on the basis of superconducting levitation, where they also state (Physica C 386, 431-437 (2003)) that the lateral stiffness of the vehicle increases with increasing mass. C. Navau et al. (Supercond. Sci. Technol. 17 (2004) 828-832) describe a model for calculating states of balance depending on the cooling position. Z. Ren et al. (Physica C 378-381 (1) 873-876 (2002)) describe a method for increasing the vertical and lateral stiffness for a linear transport system through the interaction of superconductors and permanent magnets in the vehicle. The strong repulsive forces between two equal magnetic poles are thereby utilized.
There are therefore indications from the known prior art that, on the one hand, the problem of stiffness for practical applications has been recognized, but, on the other hand, the problem has not been given sufficient consideration nor have actual solutions been identified.